Fixed-abrasive chemical-mechanical planarization of titanium nitride

ABSTRACT

Planarizing solutions, and their methods of use, for removing titanium nitride from the surface of a substrate using a fixed-abrasive planarizing pad. The planarizing solutions take the form of an etchant solution or an oxidizing solution. The etchant solutions are aqueous solutions containing an etchant and a buffer. The etchant contains one or more etching agents selective to titanium nitride. The oxidizing solutions are aqueous solutions containing an oxidizer and a buffer. The oxidizer contains one or more oxidizing agents selective to titanium nitride. In either solution, i.e., etchant or oxidizing solution, the buffer contains one or more buffering agents. Titanium nitride layers planarized in accordance with the invention may be utilized in the production of integrated circuits, and various apparatus utilizing such integrated circuits.

RELATED APPLICATIONS

[0001] This application is a Divisional of U.S. Ser. No. 09/339,735filed Jun. 24, 1999, which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present invention relates generally to methods forplanarizing semiconductor substrates, and in particular to planarizingsolutions and methods of use for removing titanium nitride from thesurface of semiconductor substrates using fixed-abrasive pads, andapparatus produced therefrom.

BACKGROUND

[0003] Chemical-Mechanical Planarizing (CMP) processes are often usedfor forming a flat surface on a semiconductor substrate in themanufacture of electronic devices. CMP processes generally removematerial from a substrate surface to create a highly planar surface. Avariety of planarizing machines have been developed to carry out suchCMP processes.

[0004] Planarizing machines for use in CMP processing generally fallinto two categories: web-format and fixed-pad format. In each case, aplanarizing pad and a planarizing solution are combined to define aplanarizing medium that mechanically and/or chemically-mechanicallyremoves material from the surface of a substrate. The planarizing padmay be of a fixed-abrasive or non-abrasive type. With a fixed-abrasivepad type, abrasive particles are fixedly bonded to a suspensionmaterial. Furthermore, the planarizing solution used with afixed-abrasive pad type is typically a “clean” solution, i.e.,substantially devoid of abrasive particles as such abrasive particlesare fixedly distributed across a planarizing surface of the planarizingpad. With a non-abrasive planarizing pad, no abrasive particles areassociated with the pad, so the abrasive particles are introduced in theplanarizing solution. Such planarizing solutions for use withnon-abrasive pad types are often slurries of both abrasive particles aswell as chemicals to aid removal of material from a substrate.

[0005] To planarize the substrate with the planarizing machine, thesurface of the substrate is first contacted against the planarizing padin the presence of the planarizing solution, i.e., a planarizing surfaceof the planarizing medium. While in contact, the substrate is then movedrelative to the planarizing surface of the planarizing medium, generallythrough lateral, rotational, revolving or orbital movement of thesubstrate, the planarizing pad or both. Lateral movement is defined asmovement in one direction. Rotational movement is defined as rotationabout an axis located at the center point of the object in motion.Revolving movement is defined as rotation about some axis located atother than the center point of the object in motion. Orbital movement isdefined as rotational or revolving movement combined with oscillation.Different types of movement may be combined, e.g., rotational movementof the substrate and rotational movement of the planarizing pad orrevolving and rotational movement of the substrate against a stationaryplanarizing pad. As is well understood in the art, such relativemovement is in a plane substantially parallel to the surface ofsubstrate. As a result, the abrasive particles and/or the chemicals inthe planarizing medium remove material from the surface of thesubstrate.

[0006] Fixed abrasive pad types are well known in the art ofsemiconductor wafer processing. See, e.g., U.S. Pat. 5,692,950 issuedDec. 2, 1997 to Rutherford et al.; U.S. Pat. No. 5,624,303 issued Apr.29, 1997 to Robinson; and U.S. Pat. No. 5,335,453 issued Aug. 9, 1994 toBaldy et al. Despite widespread recognition and acceptance of fixedabrasive pads in the processing of semiconductor wafers, effectiveplanarizing solutions for use in the fixed-abrasive planarization of anadvantageous barrier material and conductor, i.e., titanium nitride(TiN), are lacking. As a result, the customary processing forplanarizing titanium nitride utilizes abrasive slurries withnon-abrasive pad types.

[0007] One problem with CMP processing is that the planarized surface ofthe wafer may not be sufficiently uniform across the whole surface ofthe wafer. In the competitive semiconductor industry, it is alsodesirable to maximize the throughput of finished wafers. The uniformityof the planarized surface and maximization of throughput is a functionof the effectiveness and repeatability of the planarizing solutionutilized with the planarizing pad, as well as a wide array of other CMPoperating parameters. While a wide variety of planarizing solutions areavailable, these solutions are generally specific to the composition ofthe material to be removed as well as the type of planarizing pad used.For obvious reasons, planarizing solutions developed for non-abrasivepad types are ill suited for use with fixed-abrasive pad types.Therefore, it would be desirable to develop effective planarizingsolutions for planarization of titanium nitride on the surface of asemiconductor wafer for use in conjunction with fixed-abrasiveplanarizing pads.

[0008] For the reasons stated above, and for other reasons stated belowwhich will become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art formethods of planarizing titanium nitride using fixed-abrasive planarizingpads.

SUMMARY

[0009] In one embodiment, the invention provides a method of planarizingtitanium nitride on a surface of a substrate. The method includescontacting the surface of the substrate with a planarizing surface of aplanarizing medium, the planarizing medium comprising a fixed-abrasiveplanarizing pad and a clean planarizing solution. The method furtherincludes moving the surface of the substrate relative to the planarizingsurface of the planarizing medium, thereby abrading the titanium nitrideon the surface of the substrate. In another embodiment, moving thesurface of the substrate relative to the planarizing surface of theplanarizing medium comprises moving at least one of the substrate andthe planarizing surface of the planarizing medium in a manner selectedfrom the group consisting of lateral, rotational, revolving and orbital.In a further embodiment, the planarizing solution is an etchantsolution. In a still further embodiment, the planarizing solution is anoxidizing solution.

[0010] In another embodiment, a method of planarizing titanium nitrideon a surface of a substrate includes use of an etchant solution as theplanarizing solution, wherein the etchant solution contains an etchantand a buffer in aqueous solution. In one embodiment, the etchantcomprises at least one etching agent selected from the group consistingof oxalic acid, ascorbic acid and phosphoric acid. In a furtherembodiment, the buffer comprises at least one buffering agent selectedfrom the group consisting of ammonium acetate, ammonium oxalate,ammonium phosphate and diammonium phosphate. In a still furtherembodiment, the etchant solution has a pH of approximately 1 to 5. Inyet another embodiment, the etchant solution has a pH of approximately1.5 to 3.

[0011] In a further embodiment, a method of planarizing titanium nitrideon a surface of a substrate includes use of an oxidizing solution as theplanarizing solution, wherein the oxidizing solution contains anoxidizer and a buffer in aqueous solution. In one embodiment, theoxidizer comprises at least one oxidizing agent selected from the groupconsisting of ammonium persulfate, ammonium heptamolybdate, cericammonium nitrate, ceric ammonium sulfate and hydrogen peroxide. Inanother embodiment, the buffer comprises at least one buffering agentselected from the group consisting of phosphoric acid, ammonium acetate,ammonium oxalate, ammonium phosphate and diammonium phosphate. In yetanother embodiment, the oxidizing solution has a pH of approximately 1to 6. In a further embodiment, the oxidizing solution has a pH ofapproximately 1.5 to 4.

[0012] In one embodiment, the invention provides a method of planarizingtitanium nitride on a surface of a substrate. The method includescontacting the surface of the substrate with a planarizing surface of aplanarizing medium, the planarizing medium comprising a fixed-abrasiveplanarizing pad and a clean planarizing solution, wherein theplanarizing solution is an aqueous solution comprising approximately 1%to 5% by weight of oxalic acid and approximately 2% to 10% by weight ofammonium acetate. The method further includes moving the surface of thesubstrate relative to the planarizing surface of the planarizing medium,thereby abrading the titanium nitride on the surface of the substrate.

[0013] In another embodiment, the invention provides a clean aqueousplanarizing solution. The clean aqueous planarizing solution includes anetchant having at least one etching agent selected from the groupconsisting of oxalic acid, ascorbic acid and phosphoric acid, and abuffer. In one embodiment, the buffer comprises at least one bufferingagent selected from the group consisting of ammonium acetate, ammoniumoxalate, ammonium phosphate and diammonium phosphate.

[0014] In a further embodiment, the planarizing solution has a pH ofapproximately 1 to 5. In a still further embodiment, the planarizingsolution has a pH of approximately 1.5 to 3. In another embodiment, theplanarizing solution has approximately 1% to 10% by weight of theetchant and approximately 0% to 10% by weight of the buffer. In yetanother embodiment, the planarizing solution has approximately 1% to 5%by weight of the etchant and approximately 0% to 10% by weight of thebuffer. In another embodiment, the planarizing solution hasapproximately 1% to 5% by weight of oxalic acid and approximately 2% to10% by weight of ammonium acetate.

[0015] In a further embodiment, the invention provides a clean aqueousplanarizing solution. The clean aqueous planarizing solution includes anoxidizer having at least one oxidizing agent selected from the groupconsisting of ammonium persulfate, ammonium heptamolybdate, cericammonium nitrate, ceric ammonium sulfate and hydrogen peroxide, and abuffer. In one embodiment, the buffer comprises at least one bufferingagent selected from the group consisting of phosphoric acid, ammoniumacetate, ammonium oxalate, ammonium phosphate and diammonium phosphate.In another embodiment, the planarizing solution has a pH ofapproximately 1 to 6. In yet another embodiment, the planarizingsolution has a pH of approximately 1.5 to 4. In a further embodiment,the planarizing solution has approximately 1% to 10% by weight of theoxidizer and approximately 0% to 10% by weight of the buffer. In a stillfurther embodiment, the planarizing solution has approximately 1% to 5%by weight of the oxidizer and approximately 0.5% to 3% by weight of thebuffer.

[0016] Further embodiments of the invention provide planarizingsolutions and methods of removing titanium nitride of varying scope.Still further embodiments of the invention provide apparatus of varyingscope produced in accordance with methods and planarizing solutions ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIGS. 1A-1B are a cross-sectional views of a substrate with atitanium nitride layer at sequential processing stages in accordancewith an embodiment of the invention.

[0018]FIG. 2A is a schematic of a web-format planarizing machine as usedin accordance with an embodiment of the invention.

[0019]FIG. 2B is a schematic of a fixed-pad format planarizing machineas used in accordance with an embodiment of the invention.

[0020]FIG. 3 is a block diagram of an integrated circuit memory devicein accordance with an embodiment of the invention.

[0021]FIG. 4 is an elevation view of a wafer containing semiconductordies in accordance with an embodiment of the invention.

[0022]FIG. 5 is a block diagram of an exemplary circuit module inaccordance with an embodiment of the invention.

[0023]FIG. 6 is a block diagram of an exemplary memory module inaccordance with an embodiment of the invention.

[0024]FIG. 7 is a block diagram of an exemplary electronic system inaccordance with an embodiment of the invention.

[0025]FIG. 8 is a block diagram of an exemplary memory system inaccordance with an embodiment of the invention.

[0026]FIG. 9 is a block diagram of an exemplary computer system inaccordance with an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

[0027] In the following detailed description of the preferredembodiments, reference is made to the accompanying drawings which form apart hereof, and in which is shown by way of illustration specificembodiments in which the inventions may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that process or mechanical changes maybe made without departing from the scope of the present invention. Theterms wafer and substrate used previously and in the followingdescription include any base semiconductor structure. Both are to beunderstood as including silicon-on-sapphire (SOS) technology,silicon-on-insulator (SOI) technology, thin film transistor (TFT)technology, doped and undoped semiconductors, epitaxial layers ofsilicon supported by a base semiconductor, as well as othersemiconductor structures well known to one skilled in the art.Furthermore, when reference is made to a wafer or substrate in thefollowing description, previous process steps may have been utilized toform regions/junctions in the base semiconductor structure. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims.

[0028]FIG. 1A illustrates a typical substrate 12 having a first layer 1and a patterned second layer 2. In typical semiconductor processing,first layer 1 may represent a wafer of single-crystal silicon or otherbase semiconductor layer, an insulating layer separating secondpatterned layer 2 from other layers, or a combination of multiple layersformed in prior processing steps. The composition and structure of firstlayer 1 and patterned second layer 2 are trivial.

[0029] A titanium nitride layer 3 is formed on a portion of first layer1 exposed by patterned second layer 2. Titanium nitride layer 3 may beformed by chemical vapor deposition (CVD) or other processes well knownin the art. In FIG. 1B, a CMP process in accordance with an embodimentof the invention is used to remove a portion of titanium nitride layer 3and to planarize the surface of substrate 12. Titanium nitride layer 3may be utilized as a contact in an integrated circuit, e.g., where theportion of first layer 1 exposed by patterned second layer 1 forms anactive area of a semiconductor device. The integrated circuit may beutilized in the formation of various electronic devices.

[0030]FIG. 2A illustrates a web-format planarizing machine 10 forplanarizing a substrate 12 in accordance with an embodiment of theinvention. The substrate 12 has titanium nitride on its surface asillustrated in FIG. 1A. Planarizing machine 10 is used to remove atleast a portion of the titanium nitride and to planarize the surface ofsubstrate 12.

[0031] The planarizing machine 10 has a support table 14 with atop-panel 16 at a workstation where an operative portion (A) of aplanarizing pad 40 is positioned. The top-panel 16 is generally a rigidplate to provide a flat, solid surface to which a particular section ofthe planarizing pad 40 may be secured during planarization.

[0032] The planarizing machine 10 also has a plurality of rollers toguide, position and hold the planarizing pad 40 over the top-panel 16.The rollers include a supply roller 20, first and second idler rollers21 a and 21 b, first and second guide rollers 22 a and 22 b, and atake-up roller 23. The supply roller 20 carries an unused orpre-operative portion of the planarizing pad 40, and the take-up roller23 carries a used or post-operative portion of the planarizing pad 40.Additionally, the first idler roller 21 a and the first guide roller 22a stretch the planarizing pad 40 over the top-panel 16 to hold theplanarizing pad 40 stationary during operation. A motor (not shown)drives at least one of the supply roller 20 and the take-up roller 23 tosequentially advance the planarizing pad 40 across the top-panel 16. Assuch, clean pre-operative sections of the planarizing pad 40 may bequickly substituted for used sections to provide a consistent surfacefor planarizing and/or cleaning the substrate 12.

[0033] The web-format planarizing machine 10 also has a carrier assembly30 that controls and protects the substrate 12 during planarization. Thecarrier assembly 30 generally has a substrate holder 32 to pick up, holdand release the substrate 12 at appropriate stages of the planarizingcycle. A plurality of nozzles 33 attached to the substrate holder 32dispense a planarizing solution 44 onto a planarizing surface 42 of theplanarizing pad 40. The carrier assembly 30 also generally has a supportgantry 34 carrying a drive assembly 35 that translates along the gantry34.

[0034] The drive assembly 35 generally has a actuator 36, a drive shaft37 coupled to the actuator 36, and an arm 38 projecting from the driveshaft 37. The arm 38 carries the substrate holder 32 via another shaft39 such that the drive assembly 35 revolves the substrate holder 32about an axis B-B offset from a center point C-C of the substrate 12.

[0035] The planarizing pad 40 and the planarizing solution 44 define aplanarizing medium, having the planarizing surface 42, thatchemically-mechanically removes material from the surface of thesubstrate 12. The planarizing pad 40 is of a fixed-abrasive type.

[0036] In one embodiment, the planarizing solution 44 is an etchantsolution and contains an etchant of at least one etching agent and abuffer of at least one buffering agent in aqueous solution. Etchantchemistries differ significantly from oxidizer chemistries commonly usedin conventional abrasive slurries, i.e., those used with non-abrasivepad types. In etchant chemistries, the etchants are reducing agentswhich complex the titanium to facilitate removal. Preferred etchingagents include oxalic acid (HOOCCOOH.2H₂O), ascorbic acid (C₆H₈O₆), andphosphoric acid (H₃PO₄). Preferred buffering agents include ammoniumacetate (NH₄(C₂H₃O₂)), ammonium oxalate ((NH₄)₂C₂O₄.H₂O), ammoniumphosphate (NH₄H₂PO₄), and diammonium phosphate ((NH₄)₂HPO₄).

[0037] The etchant solution has a pH of approximately 1 to 5, preferablyless than approximately 3, and more preferably in the range ofapproximately 1.5 to 3. Etchant concentration in the etchant solution ispreferably in the range of approximately 1% to 10% by weight and morepreferably in the range of approximately 1% to 5% by weight.

[0038] Suitable buffer concentrations are expected to be in the range ofapproximately 0% to 10% by weight. Concentrations of etchant and buffermay fall outside the preferred ranges depending upon the combination ofetching agents and buffering agents selected. However, it is within theskill in the art to determine appropriate concentrations without undueexperimentation to achieve the desired pH ranges. The pH is defined bythe equation pH=log₁₀[H+]⁻¹, the logarithm of the reciprocal of thehydrogen-ion concentration of the solution.

[0039] In one embodiment, more than one etching agent is used as theetchant in the etchant solution. In another embodiment, the etchant inthe etchant solution consists essentially of one etching agent. In oneembodiment, more than one buffering agent is used as the buffer in theetchant solution. In another embodiment, the buffer in the etchantsolution consists essentially of one buffering agent. In still anotherembodiment, planarizing solution 44 comprises an aqueous solution havingapproximately 1% to 5% by weight of oxalic acid, approximately 2% to 10%by weight of ammonium acetate, and a pH of approximately 1.5 to 3.

[0040] The etchant solution may contain additional chemical componentsthat do not materially affect the basic and novel characteristic of thesolutions disclosed herein. Some examples include dyes, lubricants,stabilizers, surfactants, thickening agents, preservatives andantimicrobial agents to name a few. Where more than one etching agent isutilized in the etchant solution, the weight % of the etchant is basedon the combined weight of all such etching agents in relation to thetotal weight of the solution. Where more than one buffering agent isutilized in the etchant solution, the weight % of the buffer is based onthe combined weight of all such buffering agents in relation to thetotal weight of the solution.

[0041] In a further embodiment, the planarizing solution 44 is anoxidizing solution and contains an oxidizer of at least one oxidizingagent and a buffer of at least one buffering agent in aqueous solution.Preferred oxidizing agents include ammonium persulfate ((NH₄)₂S₂O₈),ammonium heptamolybdate ((NH₄)₆Mo₇O₂₄.4H₂O), ceric ammonium nitrate(Ce(NO₃)₄.2NH₄NO₃), ceric ammonium sulfate (Ce(SO₄)₂.2(NH₄)₂SO₄), andhydrogen peroxide (H₂O₂). Preferred buffering agents include phosphoricacid (H₃PO₄), ammonium acetate (NH₄(C₂H₃O₂)), ammonium oxalate((NH₄)₂C₂O₄.H₂O), ammonium phosphate (NH₄H₂PO₄), and diammoniumphosphate ((NH₄)₂HPO₄).

[0042] The oxidizing solution has a pH of approximately 1 to 6,preferably less than approximately 4, and more preferably in the rangeof approximately 1.5 to 4. Oxidizer concentration in the oxidizingsolution is preferably in the range of approximately 1% to 10% by weightand more preferably in the range of approximately 1% to 5% by weight. Anoxidizer concentration of approximately 2% by weight is furtherpreferred.

[0043] Suitable buffer concentrations are expected to be in the range ofapproximately 0% to 10% by weight. Such concentration of buffer isgenerally expected to be approximately 0.5% to 3% by weight at thepreferred oxidizer concentrations. Concentrations of oxidizer and buffermay fall outside the preferred ranges depending upon the combination ofoxidizing agents and buffering agents selected. However, it is withinthe skill in the art to determine appropriate concentrations withoutundue experimentation to achieve the desired pH ranges.

[0044] In one embodiment, more than one oxidizing agent is used as theoxidizer in the oxidizing solution. In another embodiment, the oxidizerin the oxidizing solution consists essentially of one oxidizing agent.In one embodiment, more than one buffering agent is used as the bufferin the oxidizing solution. In another embodiment, the buffer in theoxidizing solution consists essentially of one buffering agent.

[0045] The oxidizing solution may contain additional chemical componentsthat do not materially affect the basic and novel characteristic of thesolutions disclosed herein. Some examples include dyes, lubricants,stabilizers, surfactants, thickening agents, preservatives andantimicrobial agents to name a few. Where more than one oxidizing agentis utilized in the oxidizing solution, the weight % of the oxidizer isbased on the combined weight of all such oxidizing agents in relation tothe total weight of the solution. Where more than one buffering agent isutilized in the oxidizing solution, the weight % of the buffer is basedon the combined weight of all such buffering agents in relation to thetotal weight of the solution.

[0046] To planarize the substrate 12 with the planarizing machine 10,the carrier assembly 30 presses the substrate 12 against the planarizingsurface 42 of the planarizing pad 40 in the presence of the planarizingsolution 44. The drive assembly 35 then moves the substrate holder 32relative to the planarizing surface 42 to move the substrate 12 acrossthe planarizing surface 42. Movement of the substrate holder 32 is in aplane substantially parallel to the surface of substrate 12. As thesurface of the substrate 12 moves across the planarizing surface 42,material is continuously removed from the surface of the substrate 12through abrasion.

[0047] Alternatively, the planarizing machine may utilize fixed padsinstead of webs as the planarization pad. FIG. 2B illustrates afixed-pad format planarizing machine 100 for use in accordance with anembodiment of the invention. The planarizing machine 100 has a platen120, an underpad 125 attached to the platen 120, a polishing pad 140attached to the underpad 125, and a carrier assembly 130 positioned overthe polishing pad 140. A drive assembly 126 rotates the platen 120 (asindicated by arrow A), or it reciprocates the platen 120 back and forth(as indicated by arrow B). Other planarizing machines may revolve theplaten 120 about a point.

[0048] Since the polishing pad 140 is attached to the underpad 125, thepolishing pad 140 moves with the platen 120.

[0049] The carrier assembly 130 has a substrate holder 131 and resilientpad 134 to which a substrate 12 may be attached. The carrier assembly130 may be a weighted, free-floating substrate holder, or an actuatorassembly 136 maybe attached to the carrier assembly 130 to impart axialand/or rotational motion (as indicated by arrows C and D, respectively).

[0050] To planarize the substrate 12 with the planarizing machine 100,the carrier assembly 130 presses the substrate 12 surface-downwardagainst the polishing pad 140. While the surface of the substrate 12presses against the polishing pad 140, at least one of the platen 120,and therefore the planarizing surface 142, or the substrate holder 131moves relative to the other to move the substrate 12 across theplanarizing surface 142. Movement of the platen 120 and/or the substrateholder 131 are in planes substantially parallel to the surface ofsubstrate 12. As the surface of the substrate 12 moves across theplanarizing surface 142, material is continuously removed from thesurface of the substrate 12 through abrasion.

[0051] The planarizing pad 140 and the planarizing solution 44 define aplanarizing medium that chemically-mechanically removes material fromthe surface of the substrate 12. The planarizing pad 140 is of afixed-abrasive type. The planarizing machine 100 has a planarizingsolution dispenser 150 for application of the planarizing solution 44 tothe planarizing surface 142 of the planarizing medium. Planarizingsolution 44 may be an oxidizing solution or an etchant solution of theinvention.

[0052] It is recognized that the planarizing machines described aboveare typical of the major formats, i.e., web format or fixed-pad format,but that other mechanical variations and adaptations are well known inthe art. However, planarizing solutions of the invention are notdependent upon the planarizing machine format.

[0053] The various embodiments of the invention permit CMP removal oftitanium nitride using fixed-abrasive planarizing pads, regardless ofthe format of the planarizing machine. In conjunction with the variousembodiments of the invention, the CMP process may be a conditionlessplanarizing process, i.e., conditioning of the planarizing pad prior touse may be eliminated.

[0054] It will be apparent that semiconductor wafers processed inaccordance with the invention may be utilized to produce a variety ofintegrated circuit devices. It is believed that integrated circuitdevices produced in accordance with the invention exhibit lessperformance variability than devices produced using non-abrasive padtypes with abrasive slurry planarizing solutions due to reduced processvariability. The reduced process variability arises from the ability toeliminate conditioning of the planarizing pad prior to use as well aselimination of variability associated with the propensity of theabrasive particles in abrasive slurry planarizing solutions to settle oragglomerate during storage and use.

[0055] Consequently, integrated circuit devices produced in accordancewith the invention are expected to exhibit physical characteristicsdifferent from the physical characteristics inherent in planarizingtitanium nitride using non-abrasive planarizing pads in conjunction withabrasive slurry planarizing solutions due to more uniform abrasion ofthe titanium nitride on the surface of the substrate. In addition,reactive characteristics inherent in the planarizing solutions of theinvention are expected to produce physical characteristics differentfrom the physical characteristics produced by planarizing solutions ofalternate chemistries, given the differing reactive characteristicsinherent in such alternate chemistries. One typical integrated circuitdevice for use with the invention is a memory device.

[0056] Memory Devices

[0057]FIG. 3 is a simplified block diagram of a memory device accordingto one embodiment of the invention. The memory device 300 includes anarray of memory cells 302, address decoder 304, row access circuitry306, column access circuitry 308, control circuitry 310, andInput/Output circuit 312. The memory can be coupled to an externalmicroprocessor 314, or memory controller for memory accessing. Thememory receives control signals from the processor 314, such as WE*,RAS* and CAS* signals. The memory is used to store data which isaccessed via I/O lines. It will be appreciated by those skilled in theart that additional circuitry and control signals can be provided, andthat the memory device of FIG. 3 has been simplified to help focus onthe invention. The memory device 300 has at least one titanium nitridelayer planarized in accordance with the invention.

[0058] It will be understood that the above description of a DRAM(Dynamic Random Access Memory) is intended to provide a generalunderstanding of the memory and is not a complete description of all theelements and features of a DRAM. Further, the invention is equallyapplicable to any size and type of memory circuit and is not intended tobe limited to the DRAM described above. Other alternative types ofdevices include SRAM (Static Random Access Memory) or Flash memories.Additionally, the DRAM could be a synchronous DRAM commonly referred toas SGRAM (Synchronous Graphics Random Access Memory), SDRAM (SynchronousDynamic Random Access Memory), SDRAM II, and DDR SDRAM (Double Data RateSDRAM), as well as Synchlink or Rambus DRAMs.

[0059] As recognized by those skilled in the art, memory devices of thetype described herein are generally fabricated as an integrated circuitcontaining a variety of semiconductor devices. The integrated circuit issupported by a substrate. Integrated circuits are typically repeatedmultiple times on each substrate. The substrate is further processed toseparate the integrated circuits into dies as is well known in the art.

[0060] Semiconductor Dies

[0061] With reference to FIG. 4, in one embodiment, a semiconductor die710 is produced from a silicon wafer 700. A die is an individualpattern, typically rectangular, on a substrate that contains circuitry,or integrated circuit devices, to perform a specific function.Semiconductor die 710 has at least one titanium nitride layer planarizedin accordance with the invention. A semiconductor wafer will typicallycontain a repeated pattern of such dies containing the samefunctionality. Die 710 may contain circuitry for the inventive memorydevice, as discussed above. Die 710 may further contain additionalcircuitry to extend to such complex devices as a monolithic processorwith multiple functionality. Die 710 is typically packaged in aprotective casing (not shown) with leads extending therefrom (not shown)providing access to the circuitry of the die for unilateral or bilateralcommunication and control.

[0062] Circuit Modules

[0063] As shown in FIG. 5, two or more dies 710 maybe combined, with orwithout protective casing, into a circuit module 800 to enhance orextend the functionality of an individual die 710. Circuit module 800may be a combination of dies 710 representing a variety of functions, ora combination of dies 710 containing the same functionality. Someexamples of a circuit module include memory modules, device drivers,power modules, communication modems, processor modules andapplication-specific modules and may include multilayer, multichipmodules. Circuit module 800 may be a subcomponent of a variety ofelectronic systems, such as a clock, a television, a cell phone, apersonal computer, an automobile, an industrial control system, anaircraft and others. Circuit module 800 will have a variety of leads 810extending therefrom and coupled to the dies 710 providing unilateral orbilateral communication and control.

[0064]FIG. 6 shows one embodiment of a circuit module as memory module900. Memory module 900 generally depicts a Single Inline Memory Module(SIMM) or Dual Inline Memory Module (DIMM). A SIMM or DIMM is generallya printed circuit board (PCB) or other support containing a series ofmemory devices. While a SIMM will have a single in-line set of contactsor leads, a DIMM will have a set of leads on each side of the supportwith each set representing separate I/O signals. Memory module 900contains multiple memory devices 910 contained on support 915, thenumber depending upon the desired bus width and the desire for parity.Memory module 900 may contain memory devices 910 on both sides ofsupport 915. Memory module 900 accepts a command signal from an externalcontroller (not shown) on a command link 920 and provides for data inputand data output on data links 930. The command link 920 and data links930 are connected to leads 940 extending from the support 915. Leads 940are shown for conceptual purposes and are not limited to the positionsshown in FIG. 6.

[0065] Electronic Systems

[0066]FIG. 7 shows an electronic system 1000 containing one or morecircuit modules 800. Electronic system 1000 generally contains a userinterface 1010. User interface 1010 provides a user of the electronicsystem 1000 with some form of control or observation of the results ofthe electronic system 1000. Some examples of user interface 1010 includethe keyboard, pointing device, monitor and printer of a personalcomputer; the tuning dial, display and speakers of a radio; the ignitionswitch and gas pedal of an automobile; and the card reader, keypad,display and currency dispenser of an automated teller machine. Userinterface 1010 may further describe access ports provided to electronicsystem 1000. Access ports are used to connect an electronic system tothe more tangible user interface components previously exemplified. Oneor more of the circuit modules 800 may be a processor providing someform of manipulation, control or direction of inputs from or outputs touser interface 1010, or of other information either preprogrammed into,or otherwise provided to, electronic system 1000. As will be apparentfrom the lists of examples previously given, electronic system 1000 willoften contain certain mechanical components (not shown) in addition tocircuit modules 800 and user interface 1010. It will be appreciated thatthe one or more circuit modules 800 in electronic system 1000 can bereplaced by a single integrated circuit. Furthermore, electronic system1000 may be a subcomponent of a larger electronic system.

[0067]FIG. 8 shows one embodiment of an electronic system as memorysystem 1100. Memory system 1100 contains one or more memory modules 900and a memory controller 1110. Memory controller 1110 provides andcontrols a bidirectional interface between memory system 1100 and anexternal system bus 1 120. Memory system 1100 accepts a command signalfrom the external bus 1120 and relays it to the one or more memorymodules 900 on a command link 1130. Memory system 1100 provides for datainput and data output between the one or more memory modules 900 andexternal system bus 1120 on data links 1140.

[0068]FIG. 9 shows a further embodiment of an electronic system as acomputer system 1200. Computer system 1200 contains a processor 1210 anda memory system 1100 housed in a computer unit 1205. Computer system1200 is but one example of an electronic system containing anotherelectronic system, i.e., memory system 1100, as a subcomponent. Computersystem 1200 optionally contains user interface components. Depicted inFIG. 9 are a keyboard 1220, a pointing device 1230, a monitor 1240, aprinter 1250 and a bulk storage device 1260. It will be appreciated thatother components are often associated with computer system 1200 such asmodems, device driver cards, additional storage devices, etc. It willfurther be appreciated that the processor 1210 and memory system 1100 ofcomputer system 1200 can be incorporated on a single integrated circuit.Such single package processing units reduce the communication timebetween the processor and the memory circuit.

[0069] Conclusion

[0070] Planarizing solutions, and their methods of use, for removingtitanium nitride from the surface of a substrate using a fixed-abrasiveplanarizing pad type are disclosed. The planarizing solutions may takethe form of an etchant solution or an oxidizing solution. The etchantsolutions are aqueous solutions containing an etchant and a buffer. Theetchant contains one or more etching agents selective to titaniumnitride. The oxidizing solutions are aqueous solutions containing anoxidizer and a buffer. The oxidizer contains one or more oxidizingagents selective to titanium nitride. In either solution, i.e., etchantor oxidizing solution, the buffer contains one or more buffering agents.Titanium nitride layers planarized in accordance with the invention maybe utilized in the production of integrated circuits, and variousapparatus utilizing such integrated circuits.

[0071] Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.For example, other planarizing machine formats may be utilized with theinvention. Furthermore, titanium nitride layers planarized in accordancewith the invention may be utilized as conductor lines, barrier layers orother structures in addition to the contacts described herein.Accordingly, this application is intended to cover any adaptations orvariations of the invention. It is manifestly intended that thisinvention be limited only by the following claims and equivalentsthereof.

What is claimed is:
 1. A memory device, comprising: an array of memorycells; a row access circuit coupled to the array of memory cells; acolumn access circuit coupled to the array of memory cells; and anaddress decoder circuit coupled to the row access circuit and the columnaccess circuit, wherein at least one of the memory cells, the row accesscircuit, the column access circuit and the address decoder circuit havea titanium nitride layer, further wherein the titanium nitride layer isplanarized by a method comprising: abrading the titanium nitride layerwith a planarizing surface of a planarizing medium comprising afixed-abrasive planarizing pad and a clean planarizing solution.
 2. Amemory device, comprising: an array of memory cells; a row accesscircuit coupled to the array of memory cells; a column access circuitcoupled to the array of memory cells; and an address decoder circuitcoupled to the row access circuit and the column access circuit, whereinat least one of the memory cells, the row access circuit, the columnaccess circuit and the address decoder circuit have a titanium nitridelayer, the titanium nitride layer planarized by a method comprising:abrading the titanium nitride layer with a planarizing surface of aplanarizing medium comprising a fixed-abrasive planarizing pad and aclean planarizing solution, wherein the planarizing solution is anaqueous etchant solution comprising an etchant and a buffer, wherein theetchant comprises at least one etching agent selected from the groupconsisting of oxalic acid, ascorbic acid and phosphoric acid.
 3. Thememory device of claim 2, wherein the buffer comprises at least onebuffering agent selected from the group consisting of ammonium acetate,ammonium oxalate, ammonium phosphate and diammonium phosphate.
 4. Thememory device of claim 2, wherein the planarizing solution has a pH ofapproximately 1 to
 5. 5. A memory device, comprising: an array of memorycells; a row access circuit coupled to the array of memory cells; acolumn access circuit coupled to the array of memory cells; and anaddress decoder circuit coupled to the row access circuit and the columnaccess circuit, wherein at least one of the memory cells, the row accesscircuit, the column access circuit and the address decoder circuit havea titanium nitride layer, the titanium nitride layer planarized by amethod comprising: abrading the titanium nitride layer with aplanarizing surface of a planarizing medium comprising a fixed-abrasiveplanarizing pad and a clean planarizing solution, wherein theplanarizing solution is an aqueous oxidizing solution comprising anoxidizer and a buffer, wherein the oxidizer comprises at least oneoxidizing agent selected from the group consisting of ammoniumpersulfate, ammonium heptamolybdate, ceric ammonium nitrate, cericammonium sulfate and hydrogen peroxide.
 6. The memory device of claim 5,wherein the buffer comprises at least one buffering agent selected fromthe group consisting of phosphoric acid, ammonium acetate, ammoniumoxalate, ammonium phosphate and diammonium phosphate.
 7. The memorydevice of claim 5, wherein the planarizing solution has a pH ofapproximately 1 to
 6. 8. A memory device, comprising: an array of memorycells; a row access circuit coupled to the array of memory cells; acolumn access circuit coupled to the array of memory cells; and anaddress decoder circuit coupled to the row access circuit and the columnaccess circuit, wherein at least one of the memory cells, the row accesscircuit, the column access circuit and the address decoder circuit havea titanium nitride layer, the titanium nitride layer planarized by amethod comprising: abrading the titanium nitride layer with aplanarizing surface of a planarizing medium comprising a fixed-abrasiveplanarizing pad and a clean planarizing solution, wherein theplanarizing solution comprises approximately 1% to 5% by weight ofoxalic acid and approximately 2% to 10% by weight of ammonium acetate.9. A memory device, comprising: an array of memory cells; a row accesscircuit coupled to the array of memory cells; a column access circuitcoupled to the array of memory cells; and an address decoder circuitcoupled to the row access circuit and the column access circuit, whereinat least one of the memory cells, the row access circuit, the columnaccess circuit and the address decoder circuit have a titanium nitridelayer, the titanium nitride layer planarized by a method comprising:abrading the titanium nitride layer with a planarizing surface of aplanarizing medium including a fixed-abrasive planarizing pad and aclean planarizing solution, the planarizing solution having an oxidizerand a buffer, the planarizing solution being approximately 2% by weightof the oxidizer, wherein the oxidizer comprises at least one oxidizingagent selected from the group consisting of ammonium persulfate,ammonium heptamolybdate, ceric ammonium nitrate, ceric ammonium sulfateand hydrogen peroxide.
 10. A memory module, comprising: a support; aplurality of leads extending from the support; a command link coupled toat least one of the plurality of leads; a plurality of data links,wherein each data link is coupled to at least one of the plurality ofleads; and at least one memory device contained on the support andcoupled to the command link, wherein the at least one memory devicecomprises: an array of memory cells; a row access circuit coupled to thearray of memory cells; a column access circuit coupled to the array ofmemory cells; and an address decoder circuit coupled to the row accesscircuit and the column access circuit, wherein at least one of thememory cells, the row access circuit, the column access circuit and theaddress decoder circuit have a titanium nitride layer, further whereinthe titanium nitride layer is planarized by a method comprising:abrading the titanium nitride layer with a planarizing surface of aplanarizing medium comprising a fixed-abrasive planarizing pad and aclean planarizing solution.
 11. The memory module of claim 10, whereinthe planarizing solution is an aqueous etchant solution comprising anetchant and a buffer, wherein the etchant comprises at least one etchingagent selected from the group consisting of oxalic acid, ascorbic acidand phosphoric acid.
 12. The memory module of claim 11, wherein thebuffer comprises at least one buffering agent selected from the groupconsisting of ammonium acetate, ammonium oxalate, ammonium phosphate anddiammonium phosphate.
 13. The memory module of claim 11, wherein theplanarizing solution has a pH of approximately 1 to
 5. 14. The memorymodule of claim 10, wherein the planarizing solution is an aqueousoxidizing solution comprising an oxidizer and a buffer, wherein theoxidizer comprises at least one oxidizing agent selected from the groupconsisting of ammonium persulfate, ammonium heptamolybdate, cericammonium nitrate, ceric ammonium sulfate and hydrogen peroxide.
 15. Thememory module of claim 14, wherein the buffer comprises at least onebuffering agent selected from the group consisting of phosphoric acid,ammonium acetate, ammonium oxalate, ammonium phosphate and diammoniumphosphate.
 16. The memory module of claim 14, wherein the planarizingsolution has a pH of approximately 1 to
 6. 17. The memory module ofclaim 10, wherein the planarizing solution is an aqueous solutioncomprising approximately 1% to 5% by weight of oxalic acid andapproximately 2% to 10% by weight of ammonium acetate.
 18. A memorysystem, comprising: a controller; a command link coupled to thecontroller; a data link coupled to the controller; and a memory devicecoupled to the command link and the data link, wherein the memory devicecomprises: an array of memory cells; a row access circuit coupled to thearray of memory cells; a column access circuit coupled to the array ofmemory cells; and an address decoder circuit coupled to the row accesscircuit and the column access circuit, wherein at least one of thememory cells, the row access circuit, the column access circuit and theaddress decoder circuit have a titanium nitride layer, further whereinthe titanium nitride layer is planarized by a method comprising:abrading the titanium nitride layer with a planarizing surface of aplanarizing medium comprising a fixed-abrasive planarizing pad and aclean planarizing solution.
 19. The memory system of claim 18, whereinthe planarizing solution is an aqueous etchant solution comprising anetchant and a buffer, wherein the etchant comprises at least one etchingagent selected from the group consisting of oxalic acid, ascorbic acidand phosphoric acid.
 20. The memory system of claim 19, wherein thebuffer comprises at least one buffering agent selected from the groupconsisting of ammonium acetate, ammonium oxalate, ammonium phosphate anddiammonium phosphate.
 21. The memory system of claim 19, wherein theplanarizing solution has a pH of approximately 1 to
 5. 22. The memorysystem of claim 18, wherein the planarizing solution is an aqueousoxidizing solution comprising an oxidizer and a buffer, wherein theoxidizer comprises at least one oxidizing agent selected from the groupconsisting of ammonium persulfate, ammonium heptamolybdate, cericammonium nitrate, ceric ammonium sulfate and hydrogen peroxide.
 23. Thememory system of claim 22, wherein the buffer comprises at least onebuffering agent selected from the group consisting of phosphoric acid,ammonium acetate, ammonium oxalate, ammonium phosphate and diammoniumphosphate.
 24. The memory system of claim 22, wherein the planarizingsolution has a pH of approximately 1 to
 6. 25. The memory system ofclaim 18, wherein the planarizing solution is an aqueous solutioncomprising approximately 1% to 5% by weight of oxalic acid andapproximately 2% to 10% by weight of ammonium acetate.
 26. A method forforming a memory device, comprising: forming an array of memory cells;coupling a row access circuit to the array of memory cells; coupling acolumn access circuit to the array of memory cells; and coupling anaddress decoder circuit to the row access circuit and to the columnaccess circuit, wherein at least one of the memory cells, the row accesscircuit, the column access circuit and the address decoder circuit havea titanium nitride layer, the titanium nitride layer planarized by amethod comprising: abrading the titanium nitride layer with aplanarizing surface of a planarizing medium including a fixed-abrasiveplanarizing pad and a clean planarizing solution, the planarizingsolution having an etchant and a buffer, wherein the etchant includes atleast one etching agent selected from the group consisting of oxalicacid, ascorbic acid and phosphoric acid.
 27. The method of claim 26,wherein abrading the titanium nitride layer with a planarizing surfaceof a planarizing medium including a fixed-abrasive planarizing pad and aclean planarizing solution includes the buffer having at least onebuffering agent selected from the group consisting of ammonium acetate,ammonium oxalate, ammonium phosphate and diammonium phosphate.
 28. Themethod of claim 26, wherein abrading the titanium nitride layer with aplanarizing surface of a planarizing medium including a fixed-abrasiveplanarizing pad and a clean planarizing solution includes theplanarizing solution having a pH of approximately 1 to
 5. 29. A methodfor forming a memory device, comprising: forming an array of memorycells; coupling a row access circuit to the array of memory cells;coupling a column access circuit to the array of memory cells; andcoupling an address decoder circuit to the row access circuit and to thecolumn access circuit, wherein at least one of the memory cells, the rowaccess circuit, the column access circuit and the address decodercircuit have a titanium nitride layer, the titanium nitride layerplanarized by a method comprising: abrading the titanium nitride layerwith a planarizing surface of a planarizing medium including afixed-abrasive planarizing pad and a clean planarizing solution, theplanarizing solution having an oxidizer and a buffer, wherein theoxidizer includes at least one oxidizing agent selected from the groupconsisting of ammonium persulfate, ammonium heptamolybdate, cericammonium nitrate, ceric ammonium sulfate and hydrogen peroxide.
 30. Themethod of claim 29, wherein abrading the titanium nitride layer with aplanarizing surface of a planarizing medium including a fixed-abrasiveplanarizing pad and a clean planarizing solution includes the bufferhaving at least one buffering agent selected from the group consistingof phosphoric acid, ammonium acetate, ammonium oxalate, ammoniumphosphate and diammonium phosphate.
 31. The method of claim 29, whereinabrading the titanium nitride layer with a planarizing surface of aplanarizing medium including a fixed-abrasive planarizing pad and aclean planarizing solution includes the planarizing solution having a pHof approximately 1 to
 6. 32. A method for forming a memory device,comprising: forming an array of memory cells; coupling a row accesscircuit to the array of memory cells; coupling a column access circuitto the array of memory cells; and coupling an address decoder circuit tothe row access circuit and to the column access circuit, wherein atleast one of the memory cells, the row access circuit, the column accesscircuit and the address decoder circuit have a titanium nitride layer,the titanium nitride layer planarized by a method comprising: abradingthe titanium nitride layer with a planarizing surface of a planarizingmedium including a fixed-abrasive planarizing pad and a cleanplanarizing solution, the planarizing solution being approximately 1% to5% by weight of oxalic acid and approximately 2% to 10% by weight ofammonium acetate.
 33. A method for forming a memory module, comprising:providing a support; providing a plurality of leads extending from thesupport; coupling a command link to at least one of the plurality ofleads; providing a plurality of data links; coupling each data link toat least one of the plurality of leads; attaching at least one memorydevice onto the support; and coupling the at least one memory device tothe command link, wherein the at least one memory device includes atitanium nitride layer, the titanium nitride layer planarized by amethod comprising: abrading the titanium nitride layer with aplanarizing surface of a planarizing medium including a fixed-abrasiveplanarizing pad and a clean planarizing solution, the planarizingsolution having an etchant and a buffer, wherein the etchant includes atleast one etching agent selected from the group consisting of oxalicacid, ascorbic acid and phosphoric acid.
 34. The method of claim 33,wherein abrading the titanium nitride layer with a planarizing surfaceof a planarizing medium including a fixed-abrasive planarizing pad and aclean planarizing solution includes the buffer having at least onebuffering agent selected from the group consisting of ammonium acetate,ammonium oxalate, ammonium phosphate and diammonium phosphate.
 35. Themethod of claim 33, wherein abrading the titanium nitride layer with aplanarizing surface of a planarizing medium including a fixed-abrasiveplanarizing pad and a clean planarizing solution includes theplanarizing solution having a pH of approximately 1 to
 5. 36. The methodof claim 33, wherein abrading the titanium nitride layer with aplanarizing surface of a planarizing medium including a fixed-abrasiveplanarizing pad and a clean planarizing solution includes theplanarizing solution being approximately 1% to 5% by weight of oxalicacid and approximately 2% to 10% by weight of ammonium acetate.
 37. Amethod for forming a memory module, comprising: providing a support;providing a plurality of leads extending from the support; coupling acommand link to at least one of the plurality of leads; providing aplurality of data links, coupling each data link to at least one of theplurality of leads; and attaching at least one memory device onto thesupport; and coupling the at least one memory device to the commandlink, wherein the at least one memory device includes a titanium nitridelayer, the titanium nitride layer planarized by a method comprising:abrading the titanium nitride layer with a planarizing surface of aplanarizing medium including a fixed-abrasive planarizing pad and aclean planarizing solution, the planarizing solution having an oxidizerand a buffer, wherein the oxidizer includes at least one oxidizing agentselected from the group consisting of ammonium persulfate, ammoniumheptamolybdate, ceric ammonium nitrate, ceric ammonium sulfate andhydrogen peroxide.
 38. The method of claim 37, wherein abrading thetitanium nitride layer with a planarizing surface of a planarizingmedium including a fixed-abrasive planarizing pad and a cleanplanarizing solution includes the buffer having at least one bufferingagent selected from the group consisting of phosphoric acid, ammoniumacetate, ammonium oxalate, ammonium phosphate and diammonium phosphate.39. The method of claim 37, wherein abrading the titanium nitride layerwith a planarizing surface of a planarizing medium including afixed-abrasive planarizing pad and a clean planarizing solution includesthe planarizing solution having a pH of approximately 1 to
 6. 40. Amethod for forming a memory system, comprising: providing a controller;coupling a command link to the controller; coupling a data link to thecontroller; and coupling a memory device to the command link and thedata link, wherein the memory device includes a titanium nitride layer,the titanium nitride layer planarized by a method comprising: abradingthe titanium nitride layer with a planarizing surface of a planarizingmedium including a fixed-abrasive planarizing pad and a cleanplanarizing solution, the planarizing solution having an etchant and abuffer, wherein the etchant includes at least one etching agent selectedfrom the group consisting of oxalic acid, ascorbic acid and phosphoricacid.
 41. The method of claim 40, wherein abrading the titanium nitridelayer with a planarizing surface of a planarizing medium including afixed-abrasive planarizing pad and a clean planarizing solution includesthe buffer having at least one buffering agent selected from the groupconsisting of ammonium acetate, ammonium oxalate, ammonium phosphate anddiammonium phosphate.
 42. The method of claim 40, wherein abrading thetitanium nitride layer with a planarizing surface of a planarizingmedium including a fixed-abrasive planarizing pad and a cleanplanarizing solution includes the planarizing solution having a pH ofapproximately 1 to
 5. 43. The method of claim 40, wherein abrading thetitanium nitride layer with a planarizing surface of a planarizingmedium including a fixed-abrasive planarizing pad and a cleanplanarizing solution includes the planarizing solution beingapproximately 1% to 5% by weight of oxalic acid and approximately 2% to10% by weight of ammonium acetate.
 44. A method for forming a memorysystem, comprising: providing a controller; coupling a command link tothe controller; coupling a data link to the controller; and coupling amemory device to the command link and the data link, wherein the memorydevice includes a titanium nitride layer, the titanium nitride layerplanarized by a method comprising: abrading the titanium nitride layerwith a planarizing surface of a planarizing medium including afixed-abrasive planarizing pad and a clean planarizing solution, theplanarizing solution having an oxidizer and a buffer, wherein theoxidizer includes at least one oxidizing agent selected from the groupconsisting of ammonium persulfate, ammonium heptamolybdate, cericammonium nitrate, ceric ammonium sulfate and hydrogen peroxide.
 45. Themethod of claim 44, wherein abrading the titanium nitride layer with aplanarizing surface of a planarizing medium including a fixed-abrasiveplanarizing pad and a clean planarizing solution includes the bufferhaving at least one buffering agent selected from the group consistingof phosphoric acid, ammonium acetate, ammonium oxalate, ammoniumphosphate and diammonium phosphate.
 46. The method of claim 44, whereinabrading the titanium nitride layer with a planarizing surface of aplanarizing medium including a fixed-abrasive planarizing pad and aclean planarizing solution includes the planarizing solution having a pHof approximately 1 to 6.